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Image of the Week

Gaia spectra of six stars

The figure shows the spectra of six stars observed by the spectrograph on-board Gaia: the Radial Velocity Spectrometer (RVS). The spectra have been ordered from left to right and from top to bottom by spectral type (M7, K3, G0, F0, A0 and B2). This corresponds to a sequence of increasing temperatures (roughly: 3000, 4700, 6000, 7300, 10000 and 21000 Kelvin). TiO molecular transitions are visible in the atmosphere of the cool M star. As stars get hotter, the molecules are "quickly" dissociated and are not "visible" anymore. The spectra from K to F stars are dominated by three strong (ionised) Calcium lines. Many weaker lines of other chemical species are also visible. Some of the iron, silicon and titanium lines have been identified on the spectra. In the hotter A and B stars, the calcium lines are less prominent and hydrogen lines of the Paschen series become the strongest features.